Micro units are suddenly popping up across the Northeast. The idea: Young professionals want high amenities but don't wanna pay a lot. Plus, space can be tight inside dense cities. Downsizing apartments (weve seen as low as 250 SF/unit) may be the answer.

Boston's 400-year-old waterfront is often an urban lab for cutting-edge ideas, so were not surprised it has 300 micro units planned. Boston Redevelopment Authority manager for Innovation District projects Nicole Fichera tells us City planners suggest that developers build smaller apartments350 SF to 700 SFwith shared amenities at rents Millennials can afford. First on the market is Gerding Edlen's Factory 63 with 38 units, including 23 micros ranging from 350 SF to 500 SF. After a few weeks of leasing, only three of 23 innovation unitsand two of the six market rate apartmentsremain, Gerding Edlen prez Kelly Saito tells us.

The $193M, 369-apartment 100 Pier 4which includes 50 micro unitsbegan construction in December, and they're the first ones Hanover Group has built. The firm's David Hall says one challenge was creating a layout for narrow units in a building designed for traditional apartments. The solution: interlocking L-shaped units. (Which admittedly beats the Q-shaped units we proposed.) Most units are clustered on the first three floors around a business center and community area to foster impromptu meetings. Construction will be complete by Q1 '15.

ADDInc prez Fred Kramer says his firm designed 100 Pier 4, and is doing Skanska Commercial Development's 340-apartment community at the Seaport, both with micro units. There's extra initial cost to building this way, he says, since there are more kitchens, bathrooms, walls, doors, plumbing, and other components. But there are advantages: more units per GSF, youth appeal, the least costly market rate apartments, and Class-A amenities. Micro units also fetch higher rents PSF: perhaps $5.50/SF for 350 SF versus $3.50/SF for 1,000 SF.

Boston isn't the only place getting in on the craze: NYC Mayor Michael Bloomberg thinks they're so worthwhile, he kicked off adAPT NYC last summer, a pilot program to develop the new housing model. Last month it chose its development team (Monadnock Development, Actors Fund Housing Development Corp, and nARCHITECTS), and construction is now under way on the citys first micro-unit apartment building. The 55-micro unit project will sit on a City-owned site at 335 East 27thSt in Manhattan. Units will range from 250 to 370 SF and will boast 9' ceilings and Juliet balconies. (No Romeo gardens, though.) Look for completion in September 2015.